There are a number of devices for dispensing aerosols for nasal and/or oral inhalation. Such devices are now quite well known for administering medicaments to patients suffering from bronchial conditions such as, for example, bronchial asthma. The most significant problem associated with such aerosols has been the difficulty for many patients to coordinate the release of the medicament with the initiation of the inspiratory effort. Many people, for example, elderly patients and children, find this synchronization difficult. These problems are alleviated with the breath-actuated devices such as the ones disclosed in U.S. Pat. Nos. 3,636,949; 3,789,843; 3,826,413; and WO85/01880. Sometimes these devices are also referred to as inhalation-oriented aerosols or, more simply, "demand valves". Simply, these devices eliminate the need for manual coordination by actuating automatically when the patient inhales with his lips in contact with the mouthpiece. Only light negative pressure is required to trip a simple mechanism which actuates the metering valve. The device must then be reset before the metering valve may discharge again. The instant application is concerned with a breath-actuated device of this type, but embodies improvements over the devices in the aforesaid patents in that it is structured to minimize the occasions of accidental discharge and, yet, discharge can be effected with minimum effort.
A long-standing problem with breath-actuated dispenser development has been the incompatability between the strong spring required to overcome the internal aerosol valve spring for effecting discharge, and the light pressure available to impaired individuals to trigger the device. The juncture between the two aforementioned elements in the past has been so tenuous that even the surface coefficient of friction of materials had to be considered. By the introduction of an intermediate sear element and other improvements to accomplish greater mechanical advantage, this invention achieves a positive yet sensitive latching and the degree of integrity required in medical dispensing devices.